The pontine micturition center projects to sacral cord GABA immunoreactive neurons in the cat

Stimulation of the pontine micturition center (PMC) results in micturition, i.e. an immediate relaxation of the bladder sphincter and a contraction of the detrusor muscle of the bladder. Earlier studies have shown that the bladder contraction is brought about by a direct excitatory pathway from the PMC to the parasympathetic bladder motoneurons in the sacral cord. How the PMC produces the inhibition of the bladder sphincter is not known. The present study in two adult male cats demonstrates at the ultrastructural level a direct pathway from the PMC to the dorsal gray commissure of the sacral cord. More than half (55%) of these terminals made contact with gamma amino butyric acid (GABA) immunoreactive neurons or somata, the others with non-GABA immunoreactive profiles. The PMC terminals contained many round vesicles, some dense cored vesicles and exclusively asymmetric synaptic clefts, which correspond with an excitatory pathway. A concept is put forward in which this pathway produces the relaxation of the bladder sphincter during micturition.